As for internal combustion engines, there is conventionally known that combustion control based on detected information on oxygen concentration, etc. in exhaust gas which is a measuring object is effective for energy saving, emission gas purification, and others. As gas sensors for detecting the oxygen concentration, etc. in the exhaust gas, there is known a gas sensor using a sensor element constituted of solid electrolyte such as partially stabilized zirconia. Such gas sensor has variously been improved.
A known one of the above gas sensors has a concrete structure including a sensor element having a gas contact portion which will be exposed to exhaust gas, a metallic shell holding the sensor element, an outer sleeve connected at its front end with the metallic shell, a plurality of electrode output terminals electrically connected to the sensor element, a plurality of lead wires connected one each to the electrode output terminals, a separator accommodated in the outer sleeve and internally setting each electrode output terminal while insulating them from one another, and an elastic seal member formed with insertion holes through each of which each lead wire is inserted. The separator in such gas sensor includes a body part which holds a part of each lead wire and an electrode output terminal, and a flange portion of a larger diameter than that of the body part. The outer sleeve includes a small diameter portion having an inner diameter larger than the outer diameter of the body part and smaller than the outer diameter of the flange part, a large diameter portion having an inner diameter larger than the outer diameter of the flange part, and a shoulder portion connecting the small diameter portion and the large diameter part.
The separator is placed so that one surface of the flange portion engages the shoulder portion of the outer sleeve while the other surface of the flange portion is pressed and fixed by an elastic member (an urging member) fitted under pressure in the large diameter part of the outer sleeve. Thus, the separator is held in the outer sleeve. In short, the separator is fixed between the elastic member and the shoulder portion of the outer sleeve (see Patent Documents 1 and 2, for example).
[Patent Document 1] JP Published patent application No. 2001-147213
[Patent Document 2] JP Published patent application No. 2001-311713